I. Field of the Invention
The present invention relates to electric power converters. More particularly, the present invention relates to a DC voltage divider comprising capacitors, diodes and switches which is used to convert high voltage input into DC low voltage output.
II. Description of the Prior Art
AC transformers are electric power converters comprising inductance coil and core, since their invention more than one hundred years ago, they have been widely used in electrical and electronic engineering, and have occupied an almost exclusive position in the field of electric power conversion. However, they cannot meet the requirement for modern electrical equipment of small size, low material cost and low power loss.
An AC transformer is a device for bidirectional tramission, i.e., both its input and output are alternating. It is this feature that makes the AC supply mode the most widely adopted mode in power supply lines. Although the AC supply mode is convenient for power systems, AC networks are difficult to connect together. The utilization rate of the power lines is low. The loss is comparatively high, and there is no unified standards for the supply modes. Moreover, there exist phase loss and AC-DC conversion loss in the power-consuming system.
For a long time, efforts have been made to find a new converter for electric power that is superior to a transformer in its integrated specifications such as performance, volume and efficiency.
In power-consuming systems, with the development of modern micro-electronic technique, it is badly needed to provide small-sized, highly reliable low voltage and large current power sources for applications in computers, modern communication devices and other automatic devices. For this purpose, switching power sources have been developed by using high frequency control techniques to reform the transformer, and through efforts of years, accompanying the development of high frequency power devices, switching power sources that supply several watts, tens of watts, even kilowatts are being used in increasingly broader applications.
However, the switching power sources of the prior art still use transformers for voltage conversion, and transformers operating at high frequency have the problems such as high reverse peak voltage and radiation interference, and it is difficult to fabricate high power. In particular, there exists the problem of a power limit for high frequency transformers.
The number of turns of the primary and secondary coils, hence the volume, of the transformer can be reduced by elevating the operating frequency, but the inductive reactance of the transformer increases with the elevating of its operating frequency. This will restrict its power output, so elevating the operating frequency of a transformer is contradictory to increasing its power output. A tradeoff must be made. This is the reason why the practical power of switching power sources was limited to several watts to several kilowatts during 20 to 30 years after they were developed.
A switching power supply technique can elevate the efficiency of electrical equipment. It is an effective approach for saving eletric energy, but the practical application of switching power sources in some low voltage, low efficiency, large current devices that consume large amount of power such as electrolyzing, electroplating or electric welding devices still has some difficulties. The power consumed by these devices occupies a large portion of the industrial power supply, so the reforming of these devices to reduce energy consumption on a large scale is a breakthrough anxiously anticipated in the field of electrical and electronic techniques.
The key in the innovation of power sources is the electric energy converter.
As is well known, inductors and capacitors are both energy storing elements in elecrtical technology, and there exists an one-to-one correspondence between their electric characteristics. While transformers are electric energy converters made of inductors, analogous converters may be made of capacitors.
The energy stored in a conductor L or a capacitor C is, respectively EQU E.sub.L =LI.sup.2 /2 (J) EQU E.sub.C =CV.sup.2 /2 (J)
the above two equations are made equal and some certain values are substituted thereinto: EQU 1 mH.times.100.sup.2 A/2(J)=1000 .mu.F.times.100.sup.2 V/2 (J)
It can easily be seen from these formulae that the energy stored in an inductor of 1 mH when a current of 100 A flows through it is equal to that stored in a capacitor of 1000 .mu.F when it is charged to 100 V. In engineering practice, the volume of such an inductor is quite different from that of the capacitor mentioned above, the latter is small and easy to realize, while the former is bulky as can be conceived from the cross-section of the wire that allows 100 A to flow in it. Obviously, capacitors are far much superior to inductors in the function of storing energy, and this feature will manifest itself when capacitors are used to make energy converters.
Moreover, EQU Reactance of an inductor=2 .pi. f L (Ohms) EQU Reactance of a capacitor=1/[2 .pi. f C] (Ohms)
the reactance of an inductor is directly proportional to the product of inductance and frequency, it increases with the frequency, while the reactance of a capacitor is inversely proportional to the product of capacitance and frequency, it decreases when the frequency increases. This feature is what we need. It means that different output power can be obtained by changing the operating frequency of the capacitor, i.e. to get larger power output by raising the operating frequency.